This application claims the priority of German Application No. 101 46 712.5, filed Sep. 21, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a system for assisting the parking of motor vehicles in parking spaces, having at least one transmitter, which is arranged on the exterior side of the vehicle, for a transmitted signal emitted at least approximately perpendicularly to the longitudinal axis of the vehicle and limited to a small emission angle (beam angle) range, and an assigned receiver for the reflected signal.
Various known systems for assisting the parking of vehicles in parking spaces provide at least one distance sensor for measuring parking spaces. The distance sensor is mounted on the vehicle side facing the curb and, perpendicular to the driving direction, while passing, measures the length (compare German Patent Document DE 3728948 A) and optionally, in the case of limited-depth parking spaces (for example, as a result of the curb), also their depth. In this case, ultrasonic and radar distance measuring systems (such as 24 GHz systems) with conical beam lobes are used as distance sensors. Because of the cross-sectional area of the antenna, in the case of the radar systems, beam angles of approximately 60xc2x0 are used. In the case of less expensive ultrasonic systems, smaller angles can also be used. A distance sensor in this case is a transmitter/receiver having an electronic analyzing system on its output side.
In contrast to light, the described distance sensors operate using relatively large wavelengths (for example, 12.5 mm@24 GHz and 8.6 mm@40 kHz US). As a result, irradiated objects, which have a degree of roughness below this wavelength, reflect the irradiation like ideal mirrors.
Since the sensors supply only distance-related information and no directional information, objects captured in the beam cone must be positioned on the beam axis. However, the estimation of the direction by means of triangulation when two or more sensors are used will be successful only if precisely the same object site is measured. This cannot be done by means of objects reflecting in the manner of a mirror because here only perpendicularly impinging radiation is reflected back into the receiver.
The measuring of parking spaces has two basic problems: First, the geometrical shape of the parking space boundaries (box-shaped or rounded) influences the longitudinal measurement; second, there is the indistinguishability between relevant raised objects (for example, posts or vehicles) and irrelevant road-related objects (small stones, lawn rocks). Also, a differentiation between these object classes cannot be achieved by a triangulation of sensors arranged horizontally side-by-side.
The detection of the parking space depth (curb detection) requires relatively large beam angles of the sensor lobe(s). However, this reduces the positional precision and the directional accuracy for the longitudinal measuring. In the case of rounded parking space boundaries, the front of the rearward boundary is still seen in the rear view when the axis of the sensor lobe has already left it; the rear side of the forward boundary is already detected in the front view before the axis of the sensor lobe is at its height. This has the result that the measured space length seems smaller than it is. This deviation becomes more serious as a wider transmitter beam lobe is selected.
It is an object of the invention to provide a parking assistance system for parking vehicles in parking spaces of the above-mentioned type which, with low expenditures, results in reliable information concerning the actual shape of a parking space.
The invention achieves this object by providing a system for assisting the parking of motor vehicles in parking spaces, having at least one transmitter, which is arranged on the exterior side of the vehicle, for a transmitted signal emitted at least approximately perpendicularly to the longitudinal axis of the vehicle and limited to a small emission angle range, and an assigned receiver for the reflected signal. The transmitted signal is formed of two partial beams, which have approximately flat surface area emission characteristics, the two areas being situated at least approximately perpendicular with respect to one another.
An adjacent arrangement of two distance sensors 1 and 2, preferably disposed in a common housing at a forward corner point of the motor vehicle, which distance sensors 1 and 2 supply two transmitted signals of a different beam geometry and together generate a xe2x80x9ccross lobexe2x80x9d, can clearly reduce the two above-mentioned basic problems. For reasons of cost, ultrasonic sensors are preferably considered for this purpose, but naturally the principle analogously applies to radar sensors.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.